II. Drainage losses of nitrate and other nutrients

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Abstract
Drainage losses of nitrate and other nutrients were investigated at the Templeton effluent irrigation scheme (started in 1958), during the period June 1975 to May 1977. The average annual drainage was 900 mm for this period, compared with the effluent application of 840 mm and 760 mm rainfall. Losses of phosphorus in the drainage were very low, but percentage losses of all other nutrients were very high. The results indicated that after a few years' irrigation with sewage effluent no further removal of cations by the soil takes place, although at the present time sodium is displacing considerable quantities of calcium and magnesium from the soil, as a new equilibrium is established after cessation of liming in 1970. Annual losses of nitrogen in drainage were estimated to be 180 kg/ha, approximately 100 kg/ha of this being nitrogen leached from urine patches. If required, this nitrogen loss, which would give a maximum NO3-N concentration in the drainage of 20 ppm, could be greatly reduced by pasture harvesting.

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